President Bush and leaders of the 18 other NATO nations will join Russian President Vladimir Putin on Tuesday to seal a new era of cooperation between Moscow and the alliance it once regarded as an enemy. A new NATO-Russia Council to deal with terrorism and other post-September 11 threats will formally come into being at a tightly guarded summit at an airbase outside Rome.

The NATO-Russia Council will give Moscow a say in formulating joint policies with NATO on specific issues like fighting terrorism and preventing the spread of weapons of mass destruction.

Its creation comes as Russia moves closer to the West in the aftermath of the September 11 terrorist attacks on the United States and just days after Presidents Bush and Putin signed a landmark arms control accord cutting their strategic nuclear arsenals by two-thirds.

NATO officials say the new body, which will see the Russians moving into NATO headquarters in Brussels, does not give Moscow a veto over decisions made by the alliance. But they agree the new relationship between former foes is symbolic of changing times and a common resolve to face new dangers to security.

Despite the closer relationship between Moscow and the western alliance, Russia again signaled Monday that it opposes NATO's planned expansion into former Soviet lands. The alliance could admit up to seven new members at a summit in Prague next November, including the former Soviet republics of Estonia, Latvia, and Lithuania.

Upgrading NATO's relationship with Russia is aimed partly at offsetting Moscow's fears of the alliance's enlargement. But despite what NATO officials hail as the promise of the new partnership, many of Moscow's top military men are deeply suspicious of the alliance and still see it as an adversary.

Diplomats at NATO say other areas where the alliance and Russia could cooperate include peacekeeping operations, crisis management, civil defense, and sea rescue. But they acknowledge that there are no substantial projects to be undertaken in the immediate future by the 20-nation NATO-Russia Council.

NATO's embrace of Russia and its expected admission of countries that can hardly contribute to its military posture have raised questions about whether the alliance is turning into more of a political talk shop instead of a cohesive military coalition. Those questions are heightened by the "capabilities" gap between the United States, with its overwhelming military might, and most of its allies, who are either unable or unwilling to modernize their armed forces.

NATO Secretary General George Robertson warns that if NATO can no longer act as a meaningful military organization, it will be marginalized, and the United States will be free to act on its own instead of with its allies.